1) Adenine nucleotide containing two phosphate groups esterified to the sugar moiety at the 5'-position that is converted to ATP for energy for storage.

2) A nucleotide C10H15N5O10P2 composed of adenosine and two phosphate groups that is formed in living cells as an intermediate between ATP and AMP and that is reversibly converted to ATP for the storing of energy by the addition of a high-energy phosphate group.